【作者】 孙群英；

【导师】 张宏建； 周洪亮；

【作者基本信息】 浙江大学 ， 控制科学与工程， 2011， 博士

【摘要】 相对无源射频识别(RFID)技术,有源RFID技术具有通信距离远、抗干扰能力强和可携带传感器等优点。随着IC技术的发展,制约其发展的三大因素——标签的成本、功耗以及尺寸等也都将逐步得到解决。但由于RFID系统中的阅读器和标签通过相同的无线信道进行数据通信,所以存在信号冲撞的问题,特别是在有源标签密集环境中,数据冲撞可能导致严重的数据丢失,降低识别速度和增加标签的功耗等。目前,RFID防冲撞协议的研究工作主要是针对于无源RFID系统,为了解决有源RFID中的数据冲撞问题,本文首先分析了造成数据冲撞的各种因素,引入了防冲撞算法的三个评价指标,然后根据不同的冲撞因素和应用场合提出了两种防冲撞算法。最后,将提出的防冲撞算法模拟应用于“家校通”系统中。本文的研究内容及创新总结如下：(1)本文首先在有源RFID硬件平台上进行通信测试,指出了造成其数据冲撞的原因。为了进一步分析影响有源RFID通信的各种因素,采用MATLAB对其通信过程进行仿真。测试和仿真结果表明,空中信号冲撞和阅读器处理能力不足是影响其通信的两大重要因素。最后根据有源标签自身携带电池的特点,对其防冲撞算法提出了三个评价指标,分别是通信延迟、信道利用率以及标签能耗。(2)提出了一种主-从双阅读器的阅读器改进机制(MSDR),用于解决阅读器处理能力不足的问题。通过加入从阅读器,可有效降低主阅读器的处理负载,从而降低通信延迟、冲撞率和标签能耗。在本文的实验条件中,当标签个数为25时,发送周期为100ms时,相对于单阅读器机制,MSDR的识别率提高了82.9%,通讯延迟和标签能耗均降低了47.0%。当通讯负载足够大时,该机制可望将识别率提高一倍。(3)提出了一种具有预约功能的双阅读器双信道的防冲撞算法(DRDCMA),用于解决有源标签密集环境下的长数据包的空中冲撞问题。在DRDCMA中,由于预约机制的加入,将长数据包的冲撞转为短数据包的冲撞；又因为控制阅读器的加入,使数据阅读器的处理能力不受到影响。因此该算法在不增加通信延迟的基础上,有效地降低了数据冲撞,使数据信道中的识别率几乎达到100%。在本文的实验条件中,当标签个数为25时,发送周期为100ms时,相对于具有预约功能的单阅读器双信道防冲撞算法(DCMA), DRDCMA的通信延迟和标签能耗分别降低了69.1%和78.3%。(4)将主-从双阅读器机制(MSDR)模拟应用于“家校通”系统,验证了本文提出的有源RFID防冲撞算法的实用性。仿真得出,在“家校通”系统容量为500人时,保证标签寿命达到8～9年的基础上,使用单阅读器机制,阅读器的识别率为98.6418%,而使用MSDR时,阅读器识别率可高达99.9999%,较好保证了“家校通”系统的可靠性。更多还原

【Abstract】 Compared with the passive RFID, the active RFID has the advantages of longer communication distance, better anti-interference capability, carrying sensors on the board and so on. With the fast development of IC technology, all the three factors (cost, energy consumption and size of active tags) which restrict the development of the active RFID will be solved. However, data collision will happen because the readers and tags in RFID systems communicate over the shared wireless channel, especially in the dense active RFID system. This will cause serious data loss, reduce the identification speed and enlarge the energy consumption of active tags. Existing works mainly focus on the anti-collision protocols of the passive RFID. In order to solve the data collision problem in the active RFID system, this paper firstly analyses various factors that cause data collisions and proposes three evaluation criteria about the anti-collision protocols. Next, two anti-collision algorithms are proposed, facing to different collision factors and application fields. Finally, the proposed anti-collision algorithm is applied in the EduToHome system. The main contents and innovations of the research are summarized as follows.(1) Firstly, by testing the communication process on the active RFID hardware platform, the reasons that cause the data collision are shown. To analyze the factors that affect the active tag’s identification further, the simulation of its communication process is made using MATLAB. The results of experimental test and simulation indicate that wireless signals overlapping in the air and the insufficient processing ability of reader are the two most important influencing factors. Finally, Considering that the active RFID has batteries on the tag’s board, three criteria are proposed to evaluate the anti-collision protocols, which are respectively communication latency, anti-collision rate, and energy consumption of the active tag.(2) A master-slave dual reader anti-collision mechanism (MSDR) is proposed, which can enhance the processing ability of the reader. By adding the slave reader, the processing load of the master reader is reduced efficiently. Therefore, the access latency, collision rate, and energy consumption of the active tag are all reduced. In the experiment environment, when the number of tags is 25 and the transmitting cycle is 100ms, compared with the single reader mechanism, MSDR can improve the rate by 82.9%, and reduce the access latency and tag’s energy consumption by 47.0%. When the communication load is huge enough, the rate of identification can be nearly doubled.(3) A dual-reader dual-channel protocol (DRDCMA) with the appointment function is brought in, which can address the air collision problem of the long data packet in the dense active RFID system. In DRDCMA, with the appointment function, the long data packet collision is turned into the short data packet collision. Because of the introduction of the control reader, the processing ability of the data reader will not be influenced by the appointment. Therefore, the access latency is not increased, the data collisions reduced efficiently, and the identification rate in the data channel reaches nearly 100%. In the experiment, when the number of tags is 25 and the transmitting cycle is 100ms. the access latency and energy consumption are reduced by 69.1% and 78.3%, respectively, compared with the dual-channel protocol with the appointment function (DCMA).(4) MSDR is applied in the EduToHome system simulatively, which verifies the practicality of the proposed active RFID anti-collision algorithm. The simulation shows that when the capacity of the EduToHome system is 500, in premise of that the tags’ life-time is 8-9 years, the reader’s identification rate is 98.6418% with the single reader mechanism, while it can reach up to 99.9999% with MSDR. Therefore, MSDR can well guarantee the reliability of the EduToHome system.更多还原